The present invention relates to a method for initially setting the position of an origin which serves as a reference for positioning operation in a link actuator for which a precise and wide operating range is required as in a medical device, an industrial device, or the like. The present invention also relates to a link actuator which can appropriately perform the initial setting.
One example of a working device equipped with a link mechanism body is disclosed in Japanese Patent Publication No. 2000-94245, and one example of a link actuator used in a medical device, an industrial device, or the like is disclosed in U.S. Pat. No. 5,893,296.
In the link mechanism body of Japanese Patent Publication No. 2000-94245, the operating angle of each link is small. Therefore, in order to increase the operating range of the travelling plate, the link mechanism body is required to have an increased link length. Accordingly, a problem has been found that the dimensions of the mechanism as a whole increase and the apparatus tends to be bulky in size. Also, if the link length is increased, the rigidity of the mechanism as a whole tends to be lowered. For this reason, there has also been a problem that the weight of a tool mounted on the travelling plate, that is, the weight capacity of the travelling plate is limited to a small value. For these reasons, it is difficult to use the link mechanism body in a medical device or the like which requires the link mechanism body to be compact in size and to operate in a precise and wide operating range.
The link actuator of U.S. Pat. No. 5,893,296 is structured to include three or more trinodal chain link mechanisms, thereby being able to operate in a precise and wide operating range, although the link actuator is compact in size. However, even in the link actuator having the above structure, it is difficult to completely eliminate backlash caused by the mechanisms such as, for example, meshing portions between gears. Thus, occurrence of deviation in positioning caused by this backlash during operations has been inevitable. Moreover, in accordance with increase of the total operating time, backlash in drive mechanism sections such as gears or the like increases, and additionally, positioning accuracy is lowered under the influence of the backlash.